Method and equipment for performing flow shaping that maintains service quality in packet-switched telecommunications

ABSTRACT

The invention relates to a method and equipment for performing flow shaping that maintains service quality in packet-switched telecommunications. Using the method according to the invention, the speed properties (CIR, PIR, CBS) of an aggregate flow (A) can be monitored and limited in a situation, in which the aggregate flow contains delay-critical traffic (V1), the forwarding of packets representing which cannot be delayed. The invention is based on the fact that, when forwarding packets representing the aggregate flow, a variable is updated, the value of which expresses the earliest permitted moment, at which a packet, representing traffic (V2) other than the delay-critical traffic, can be forwarded. In that case, the transfer speed of the traffic (V2) other than delay-critical traffic adapts to the variations in the transfer speed of the delay-critical traffic, allowing the speed properties of the aggregate flow to be monitored and limited.

The present invention relates to a method, according to Claim 1, for performing flow shaping that maintains flow shaping in packet-switched telecommunications.

The invention also relates to equipment, according to Claim 3, for performing flow shaping that maintains service quality in packet-switched telecommunications.

In this publication, the following abbreviations are used in the depiction of both the prior art and the invention: CBS Committed Burst Size (greatest permitted burst size [bit]), when exceeding the committed information flow, CIR Committed Information Rate (greatest permitted mean traffic speed [bit/s]), CoS Class of Service FIFO First In, First Out discipline, MP Measuring Point, in which the speed characteristics of the traffic flow are measured (e.g., mean traffic speed, momentary traffic speed, bust size), PIR Peak Information Rate (greatest permitted momentary traffic speed [bit/s]), PKS Packet size in bits, V1, V2, . . . Traffic flow 1, 2, . . . , VTS The earliest moment in time, after which the next packet representing a specific traffic flow may be forwarded, in order that not even one rule set for a speed property of the traffic flow in question will be broken (Valid Time to Send), VTS_CIR The earliest moment in time, after which the next packet may be forwarded, in order that the greatest permitted mean speed and/or the greatest permitted burst size will not be exceeded, VTS_PIR The earliest moment in time, after which the next packet may be forwarded, in order that the greatest permitted momentary speed will not be exceeded.

In packet-switched telecommunications systems, it is often advantageous if the packets being transmitted are classified indifferent service classes (CoS) according, on the one hand, to the requirements of the applications using the telecommunications service and, on the other, to the kind of service-quality agreements that the telecommunications service provider (Service Provider) has made with its customers. For example, in a telephone application (Voice over Internet), it is essential for the data-transfer delay and the variation of the delay to remain below the permitted limit values. The permitted limit-values are often defined in a service-quality agreement. However, when downloading www pages, for example, the data-transfer delay and its variation are significantly less critical quantities.

It is often wished to monitor and limit the speed properties of a traffic flow formed from packets to be transferred. Such a situation occurs, for example, if it is wished to reserve a specific portion of the data-transmission capacity of a transfer link for a specific customer, so that the traffic of the customer in question will not be permitted to exceed the transmission capacity reserved for him. The traffic flow being examined thus consists of packets representing the traffic of the customer in question, which can represent differ service classes. In other words, a virtual transfer link is formed to the customer in question, the transmission capacity of which is part of the capacity of the physical transfer link used for the implementation. A speed property can refer to, for example, the mean speed of the traffic (CIR), the burst size (CBS), by which the mean speed can be momentarily exceeded, or the momentary speed (PIR). Taken more generally, the traffic flow can consist of, for example, packets to be routed to a specific transfer link, packets with a specific source address and sent by a specific end user, or packets that belong to a specific class of service (CoS) and are to be routed to a specific transfer link. In the rest of this publication, a system, which can be used to monitor and limit the speed properties of a traffic flow, will be referred to as a ‘shaper’ and the operation, in which the speed properties of a traffic flow are monitored and limited, will be referred to as ‘shaping’.

The following examines a system, to which two traffic flows V1 and V2 arrive. The traffic flow V1 arriving in the system represents delay-critical traffic (e.g., Voice over Internet), for which a greatest permitted delay and delay variation have been defined. The traffic flow V2 arriving in the system represents traffic that is considerably less delay-critical than that of flow V1. The traffic flows V1 and V2 are multiplexed to a common transfer link S leaving the system. Multiplexing is performed on the basis of priority, in such a way that the packets representing the traffic flow V1 are forwarded with a higher priority than the packets representing the traffic flow V2, because traffic flow V1 represents delay-critical traffic. It is wished to monitor and limit the speed properties of the aggregate flow A being transmitted to the transfer link S.

FIG. 1 shows one way, according to the prior art, of monitoring and limiting the speed properties of the aggregate flow A. In the following examination that elucidates the matter, the term speed properties is used to include mean speed (CIR [bit/s]), burst size (CBS [bit]), by which the mean speed can be exceeded temporarily, and momentary speed (PIR [bit/s]). When packets are begun to be transferred past the measurement point (MP) marked in FIG. 1 (i.e. when the first bit of the packet being transferred passes the point MP), the values of the variables VTS_CIR and VTS_PIR are calculated for the next packet. VTS_CIR gives the earliest permitted moment in time, when the next packet can be begun to be transferred past MP, in order not to exceed the CIR or the CBS restrictions. Correspondingly, VTS_PIR gives the earliest permitted moment in time, when the next packet can be begun to be transferred past MP, in order not to exceed the PIR restriction. The equations 1 and 2 show the principle generally used for calculating the VST_CIR and the VTS_PIR values. VTS _(—) CIR _(next)=max(t−CBS/CIR, VTS _(—) CIR _(ed))+PKS _(ed) /CIR,   (1) and VRS _(—) PIR _(next)=max(t, VTS_PIR_(ed))+PKS _(ed) /PIR,   (2) in which t is the time, PKS is the size of the packet in bits, the sub-index ‘next’ refers to the next packet and the sub-index ‘ed’ refers to the packet, the first bit of which is transferred past point MP at the moment t.

When all the speed properties are taken into account, the earliest permitted moment (VTS), when the next packet can begin to be transferred past point MP, is obtained from equation 3. VTS=max(VTS _(—) CIR, VTS _(—) PIR).   (3)

The multiplexer SP only selects the next packet to be transferred, once enough time has elapsed that t [$]≧VTS.

A problem in the system shown in FIG. 1 is that the packets representing the traffic flow V1 too are delayed. This can cause the transmission delays of the packets representing the traffic flow V1 to increase over the permitted limit values. This has resulted in the system shown in FIG. 2, in which the FIFO queue 2, which stores the packets representing the traffic flow V2, offers the packets to the multiplexer SP only once enough time has elapsed that t≧VTS, becoming established as the system generally used according to the prior art. The system shown in FIG. 2 does not delay the packets representing the traffic flow V1, and thus does not diminish the delay properties of the traffic flow V1. In other words, the quality of service required for the traffic flow V1 is maintained. The functioning of the system depends on the assumption that the speed properties of the traffic flow V1 arriving at the system are sufficiently within the desired limits. In that case, the speed properties of the aggregate flow A will be sufficiently within the desired limits, because the speed limits of the other sub-factor—the traffic flow V2—are monitored and limited. Naturally, one problem is the uncertainty concerning the speed properties of the traffic flow V1 and another problem is the fact that temporal variation in the speed properties of the traffic flow V1 appears directly as a temporal variation in the speed properties of the aggregate flow A, FIG. 3.

The present invention is intended to eliminate the defects of the prior art disclosed above and for this purpose create an entirely new type of method and equipment for performing flow shaping that retains the quality of service in packet-switched telecommunications. The aim of the invention is a method and equipment for performing shaping in such a way as to avoid the aforementioned problems relating to the prior art.

The method according to the invention is characterized by what is stated in the characterizing portion of Claim 1.

The equipment according to the invention is, in turn, characterized by what is stated in the characterizing portion of Claim 5.

In the following, the invention is examined in greater detail with the aid of examples according to the accompanying figures.

FIG. 1 shows a block diagram of one system according to the prior art, by means of which the speed properties of an aggregate flow A can be monitored and limited.

FIG. 2 shows a block diagram of a second system according to the prior art, by means of which the speed properties of an aggregate flow A can be monitored and limited.

FIG. 3 shows the operation of the system according to FIG. 2.

FIG. 4 shows a block diagram of one system according to the invention, by means of which the speed properties of an aggregate flow A can be monitored and limited.

FIG. 5 shows the operation of a system according to the invention.

The theoretical basis of the method according to the invention will become apparent from the following examination.

Traditionally, flow-shaping machinery operates in such a way that, in connection with the traffic flows being monitored, the corresponding VTS values are updated, for example, as shown in equations 1, 2, and 3 and, if necessary, the forwarding of the packets relating to the traffic flows being monitored is delayed. The method according to the invention is characterized by the fact that, in connection with one or more specific traffic flows, the shaping machinery operates in such a way that it only updates the VTS values, but does not delay the packets representing the relevant traffic flows. The delaying performed on the basis of the relevant VTS values is applied to the forwarding of packets representing the other traffic flows.

The operation of the method according to the invention will be examined with the aid of one system according to the invention, shown in FIG. 4. When a packet representing the traffic flow V1 is transferred past the measurement point MP1, the VTS values are updated in a manner according to equations 1, 2, and 3. Correspondingly, when transferring a packet representing the traffic flow V2 past the measurement point MP2, the said VTS values are updated in a manner according to equations 1, 2, and 3. No restrictions are set for the FIFO queue 1, which stores packets representing the traffic flow V1, as to when the FIFO queue 1 can offer packets to the input x of the multiplexer SP. The FIFO queue 2 storing packets representing the traffic flow V2, on the other hand, can only offer packets to the input y of the multiplexer SP, if the moment of time t being examined is at least as great as the VTS value (t≧VTS). This means that the transmission speed of the traffic flow V2 is effectively limited in a situation, in which the transmission speed of the traffic flow V1 is high, as the VTS value will increase rapidly purely due to the effect of the forwarding of packets representing the traffic flow V1. Correspondingly, in a situation, in which the transmission speed of the traffic flow V1 is low, the transmission speed of the traffic flow V2 will be limited considerably less, as the forwarding of packets representing the traffic flow V1 will have little effect in increasing the VTS values. Thus, the operation shown in FIG. 5 will be achieved, in which the transmission speed of the traffic flow V2 will adapt to variations in the transmission speed of the traffic flow V1. The speed properties of the aggregate flow A can thus be monitored and limited, without requiring packets representing the traffic flow V1 to be delayed.

The method according to the invention can also be used when some other multiplexer than one based on priority is used, for example, a weight-coefficient-based multiplexer (WFQ, Weighted Fair Queuing) [1].

REFERENCES

-   [1] Pawan Goyal, Harric M. Vin, Haichen Cheng. Start-time Fair     Queuing: A Scheduling Algorithm for Integrated Services Packet     Switching Networks. Technical Report TR-96-02, Department of     Computer Sciences, University of Texas Austin. 

1. A method for performing flow shaping that maintains service quality in packet-switched telecommunications, in which method digital information is transferred as constant or variable-length packets, the packets arrive in the system as at least two separate traffic flows (V1−VL, traffic flow), the packets arriving in the system are forwarded from the system along one or more transfer links (S), characterized in that as a result of the forwarding of packet representing a specific traffic flow (V1) arriving in the system, at least one such variable (VTS) is updated, which is also updated as a result of the forwarding of packets representing a specific second traffic flow (V2) arriving in the system, and a packet representing the first said traffic flow (V1) is forwarded independently of the said variable (VTS), and the earliest permitted moment of forwarding a packet representing the said second traffic flow (V2) is defined, at least partly, on the basis on the said variable (VTS).
 2. A method according to claim 1, characterized in that the earliest permitted moment of forwarding a packet representing the said second traffic flow (V2) is defined solely on the basis of the said variable (VTS).
 3. A method according to claim 1 or 2, characterized in that the VTS value (Valid Time to Send) is used as the said variable.
 4. A method according to any of the above claims, characterized in that packets representing the first said traffic flow (V1) are forwarded from the system at a higher priority (Strict Priority) that packets representing the said second traffic flow (V2).
 5. Equipment for performing flow shaping that maintains service quality in packet-switched telecommunications, in which the equipment includes means for receiving constant or variable-length packets carrying digital information, means for classifying a packet arriving in the system as representing one of the traffic flows (V1, V2) (traffic flow) arriving in the system, and means for forwarding packets to an outgoing link or links (S), characterized in that the equipment includes means, with the aid of which it is possible to update, as a result of the forwarding of a packet representing a specific traffic flow (V1), such a variable (VTS) that can also be updated as a result of the forwarding of a packet representing a specific second traffic flow (V2), and with the aid of which means a packet representing the first said traffic flow (V1) can be forwarded independently of the said variable (VTS), and with the aid of which means it is possible to define the earliest permitted moment, at which a packet representing the second said traffic flow (V2) can be forwarded, at least partly on the basis of the said variable (VTS).
 6. Equipment according to claim 5, characterized in that the equipment includes means, with the aid of which it is possible to define the earliest permitted moment, at which a packet representing the second said traffic flow (V2) can be forwarded, solely on the basis of the said variable (VTS).
 7. Equipment according to claim 5 or 6, characterized in that the equipment includes means, with the aid of which the VTS (Valid Time to Send) value can be used as the variable.
 8. Equipment according to any of the above claims, characterized in that the equipment includes means, with the aid of which packets representing the said first traffic flow (V1) can be forwarded from the system at a higher priority (Strict Priority) than packets representing the said second traffic flow (V2). 